Pressure indicator



Dec. 13, 1955 c. c. JONES PRESSURE INDICATOR Filed Oct. 23, 1951 ll; v en7B r CyR/L C. Ton 5 I I W m Afro r11 V6 Patented Dec. 13, 1955 ice PRESSURE INDICATOR Cyril C. Jones, Basingstoke, England, assignor to Kelvin & Hughes Limited, Hillington, Glasgow, England Application October 23, 1951, Serial No. 252,777

Claims priority, application Great Britain October 24, 1954) 6 Claims. (Cl. 73-397) This invention relates to instruments operated by pressure actuated capsules (or bellows or Sylphons) and is applicable both to evacuated and open types of capsules.

When large deflections are required the overload characteristic results in reduced sensitivity. Also when the instrument indications are required to obey a specified relation to the applied pressure, difiiculty is experienced in matching the required characteristic at the extreme end of the range.

According to the present invention one or more main pressure actuated capsules actuate an indicator means or other actuated means and over only a part of its range at least one additional capsule operatively controls said means to correct its movement.

In one constructional form of the invention, the main capsule applies its movement to a bridge device which bridges'th e additional capsule, and the bridge device operates the indicator through means including a resilient member to which additional movement is applied by said additional capsule near the limit of the externally low pressure range of the instrument.

The invention will now be more fully described by way of example with reference to the accompanying drawings wherein:

Figure l is a view partly in front elevation and partly in section of an altimeter made in accordance with the invention; and

Figure 2 is a view of the altimeter partly in side elevation and partly in section.

The altimeter is generally similar in construction to the instrument described in the specification of British Patent No. 481,941 and has a frame 10 fixed to a peripherally toothed ring 11 which is to be mounted to rotate in a channel of a casing (not shown).

The altimeter is provided with two main capsules 13, 14 and an additional capsule 15. The capsules 13, 14 are attached together axially by a stud 16. The capsule 13 is mounted axially on a mounting stud 17 carried by a clamp 18' that is mounted on the frame 10. A bimetallic temperature compensating device 20 is carried on the stud 17 by means of nuts 21 and has arms 22, 23 that act through toggle links 26, 27 on a disc 28 on the free end of the additional capsule.

The capsules 14, are connected together axially by studs 30, 31 between which is fixed a part 32 of a bridge member. This part 32 extends between these capsules to diametrically opposite positions where it continues in the form of two limbs 33, 34 parallel with the axis of the capsules. These limbs carry continuations 35, 36 that continue at 37, 38 parallel to the part 32. The parts 32, 33, 34, 35, 36, 37, 38 constitute a substantially rigid bridge that extends around the capsule 15. A resilient member 40 in the form of a leaf spring is attached at one end by screws 41 to the limb 38 and its other or free end has a block like extension 43 which normally rests on the opposite limb 37 with a pressure due to the leaf spring 40 suitably selected in comparison with the counter pressure which the capsule 15'can exert.

The block 43 carries a screw 42 which can be adjusted into proximity with the disc 28.

A link 44 is pivotally attached at 45 to the block 42 and at 46 to a link or lever rod 47 that passes through a rock-shaft 48 which is carried in bearings at 50, 51. This rock-shaft has the inner end of a counter balance spring 52 attached thereto, the other end of said spring being fixed by a screw 53 to a part of the frame 10.

An inertia compensator arm 56 is pivotally mounted at 56 on the frame 10 and is connected by a link 57 and pin 58 to the rock-shaft 48.

The rock-shaft 48 carries a toothed sector 60 which meshes with a pinion 61 that is fixed to a toothed wheel 62. An indicator means is provided in the form of a pointer 63 cooperating with a scale (not shown). The pointer 63 is carried on a spindle 64 that carries a pinion 65 in mesh with the toothed wheel 62 whereby the move ments of the capsules are applied through the parts described to the pointer.

The capsules are almost completely evacuated. When atmospheric pressure decreases on the increase in altitude of an aeroplane the main capsules move the bridge piece to the left as viewed in Figure l.

The upper range of the altimeter is say 60,000 feet. Because of the logarithmic relation between pressure change and height, difiiculty is normally experienced in obtaining suflicient deflection of the pointer at the higher altitudes. The two main capsules 13, 14 serve to operate up to say 50,000 feet and all three capsules are operated from 50,000 feet upwards. For example, up to about 50,000 feet the main capsules operate the pointer through the bridge piece, spring, linkage and rock-shaft and at thev same time carry the additional capsule with them. At about 50,000 feet the disc 28 on the additional capsule contacts the screw 42 on the spring 40 and lifts the free end of the latter off the bridge piece thereby applying additional movement to the linkage, rock-shaft and pointer. The spring must be of suflicient stiffness to overcome any opposing effect introduced via the linkage by the counter balance spring 52.

For setting the instrument, it is first calibrated up to, say, 50,000 feet with the screw 42 unscrewed. Under this condition the main capsules only contribute useful deflection to the linkage. When a good calibration has been obtained, the screw is screwed in to make contact at a particular altitude with the disc 28 thus making the deflection of the latter available. If this extra deflection is required at 50,000 feet then the screw will make contact.

with the disc before 50,000 feet is reached and the addi tional capsule will have to build up suflicient pressure to lift the spring from the bridge piece at the desired altitude. This ensures that the changeover from two to three capsules is carried out smoothly.

It is possible to apply the device of the invention with an increase of about inch only in overall height. This includes the normal Kollsman type of temperature com-- pensation of the stack and three standard 50,000 capsules as shown.

The device may be applied to other types of pressure. operated instruments, e. g. air speed indicators, where extra.

sensitivity is required at the extreme range.

Advantages can also be taken of the fact that above: a specified altitude the spring 40 and linkage 44, 47, forms a three bar linkage so that by the correct choice of thev relative lengths of these three components a better approximation to the required law may be obtained.

What we claim is:

1. An instrument having an indicator element, actuating means for actuating said element, a first pressure actuated capsule, a second pressure actuated capsule carried by the first capsule so that the second capsule is moved bodily in accordance with the variations of the first capsule, a bridge device connected with the first capsule and extending over the second capsule, motion transmitting means resiliently attached to said bridge device and connected to said actuating means to yieldingly transmit motion to said actuating means, said second capsule having a motion-transmitting means that is positioned to be moved into operative relation with the first-mentioned motion-transmitting means by the movable wall of the capsule only when the pressure to be measured is within a predetermined range, wherein the bridge device has a part located between the first capsule and the second capsule and said part has two limbs at its opposite ends which extend around the second capsule, and the resilient means consists of a leaf spring that is attached at one end to one of said limbs and at its other end engages the other limb so that the free end of the spring is pushed away from the limb by the motion transmitting means of said second capsule when in operative relation with the motion transmitting means attached to said bridge, said spring being attached to said actuating means.

2. An instrument having an indicator element, actuating means for actuating said element, a first pressure actuated capsule, a second pressure actuated capsule carried by the first capsule so that the second capsule is moved bodily in accordance with the variations of the first capsule, a bridge device connected with the first capsule and extending over the second capsule, motion transmitting means resiliently attached to said bridge device and connected to said actuating means to yieldingly transmit motion to said actuating means, said second capsule having a motion-transmitting means that is positioned to be moved into operative relation with the first-mentioned motion-transmitting means by the movable wall of the capsule only when the pressure to be measured is within a predetermined range, wherein the bridge device has a part located between the first capsule and the second capsule and said part has two limbs at its opposite ends which extend around the second capsule, and the resilient means consists of a leaf spring that is attached at one end to one of said limbs and at its other end engages the other limb so that the free end of the spring is pushed away from the limb by the motion transmitting means of said second capsule when in operative relation with the motion transmitting means attached to said bridge, said spring being attached to said actuating means, said actuating means including a linkage connected to the spring, said spring and linkage forming a three bar linkage, the relative lengths of which bars are selected to achieve a close approximation to the required characteristics of the instrument.

3. An instrument having an indicator element, actuating means for actuating said element, a first pressure actuated capsule, a second pressure actuated capsule carried by the first capsule so that the second capsule is moved bodily in accordance with the variations of the first capsule, a bridge device connected with the first capsule and extending over the second capsule, motion transmitting means resiliently attached to said bridge device and connected to said actuating means to yieldingly transmit motion to said actuating means, said second capsule having a motion-transmitting means that is positioned to be moved into operative relation with the first-mentioned motion-transmitting means by the movable wall of the capsule only when the pressure to be measured is within a predetermined range, wherein the bridge device has a part located between the first capsule and the second capsule and said part has two limbs at its opposite ends which extend around the second capsule, and the resilient means consists of a leaf spring that is attached at one end to one of said limbs and at its other end engages the other limb so that the free end of the spring is pushed away from the limb by the motion transmitting means of said second capsule when in operative relation with the motion transmitting means attached to said bridge, said spring being attached to said actuating means, said spring carrying an adjustable screw that is engaged by the second capsule when the latter becomes operative.

4. A pressure measuring instrument having an indicator element movable over a graduated scale, movable actuating means for actuating said element, a first pressure capsule having a movable wall, movable in response to the pressure to be measured, a second pressure actuated capsule carried by the first so that the second capsule is moved bodily in accordance with the motion of said wall of the first capsule, said second capsule also having a movable wall movable in response to the pressure to be measured, a bridge device carried by said movable wall of the first capsule so as to be moved thereby, and extending over the second capsule, motion transmitting means resiliently attached to said bridge device and connected to said actuating means to yieldingly transmit motion to said actuating means, said second capsule having a motion transmitting means that is positioned to be moved into operative relation with the first mentioned motion transmitting means by the movable wall of the second capsule only when the pressure to be measured is within a certain range.

5. A pressure-measuring instrument having an indicator element movable over a graduated scale, movable actuating means for actuating said element, a first capsule having a wall movable over the entire range of the instrument in response to pressure to be measured, a second capsule carried by the first capsule and bodily movable with the movable wall of said first capsule, said second capsule having a wall movable over the whole pressure range of the instrument, said walls of said capsules being thus movable independently of each other over the entire pressure range, said actuating means including a first element operatively connected to the movable wall of said first capsule to initially transmit motion of the movable wall of said first capsule to said indicator element over a predetermined range of movement of the movable wall of said first capsule, said actuating means also including a second element arranged to be moved by the movable wall of the said second capsule to transmit motion to said indicator element only in a range of movement of the capsule walls beyond the first mentioned range of movement, said second element being adapted to transmit motion to said actuating means independently of the motion transmitted by said first element to said actuating means.

6. A pressure measuring instrument comprising two capsules each having a wall moable in response to pressure, one capsule being mounted so as to be bodily moved by motion of the movable wall of the other capsule, said capsules being expandable independently of each other in response to ambient pressure, an actuating element movable by the wall of said one capsule to actuate indicator means, and an actuating element movable by the wall of said other capsule to actuate said indicator means, said other capsule being efiective to provide motion initially of its actuating element to actuate said indicator means, said first-mentioned capsule being moved by said Wall of said other capsule into a position to motivate its actuating element subsequently to augment the actuation of said indicator means.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,666 Angst July 20, 1943 2,565,472 Castel et al Aug. 28, 1951 FOREIGN PATENTS 145,462 Great Britain Sept. 15, 1921 361,545 Germany Oct. 17, 1922 552,294 Great Britain Mar. 31, 1943 

